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The fossil record and faunal succession form the basis of the science of biostratigraphy or determining the age of rocks based on embedded fossils. For the first 150 years of geology , biostratigraphy and superposition were the only means for determining the relative age of rocks.
Hence the fossil record is very incomplete, increasingly so further back in time. Despite this, it is often adequate to illustrate the broader patterns of life's history. [58] There are also biases in the fossil record: different environments are more favorable to the preservation of different types of organism or parts of organisms. [59]
The combination of continental drift and evolution can sometimes be used to predict what will be found in the fossil record. Glossopteris is an extinct species of seed fern plants from the Permian. Glossopteris appears in the fossil record around the beginning of the Permian on the ancient continent of Gondwana. [155]
Stromatolites are a major constituent of the fossil record of the first forms of life on Earth. [24] They peaked about 1.25 billion years ago (Ga) [22] and subsequently declined in abundance and diversity, [25] so that by the start of the Cambrian they had fallen to 20% of their peak.
The chimpanzee–human divergence likely took place around 10 to 7 million years ago. [1] The list of fossils begins with Graecopithecus, dated some 7.2 million years ago, which may or may not still be ancestral to both the human and the chimpanzee lineage.
However, current evidence in the fossil record supports the concept of mass extinctions. As a result, the general idea of catastrophism has re-emerged as a valid hypothesis for at least some of the rapid changes in life forms that appear in the fossil records. A very large number of fossils have now been discovered and identified.
It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record.
Comparing the record about the discordance in the record to the full rock column shows the non-occurrence of the missing species and that portion of the local rock record, from the early part of the middle Eocene is missing there. This is one form of discordancy and the means geologists use to compensate for local variations in the rock record.